This invention relates to tachographs for motor vehicles, and particularly to tachographs for use on motor vehicles, such as trucks driven by professional drivers, for the purpose of recording data such as the time of day, the date, the driver's service hours, the driver's driving times, the driver's standby times, the driver's rest times, the distance driven, and the speed driven.
The invention is particularly directed to such tachographs using various signal transmitters for obtaining the data, and a microprocessor for utilizing the data to determine other data such as distance and speed.
Tachographs of this type are often legally prescribed for various types of motor vehicles to acquire data describing the transport services being performed in such a way that the data satisfactorily takes into account the interest of the drivers, their employers, and the regulatory agencies involved. The required data should offer the drivers proof of service or work time which is easily readable at any time, that is, readable at any time without technical input, preferably in the form of "hard", i.e. printed, copy. The data should enable those in charge of a carpark or garage to easily monitor the business use of the vehicles, and the organizational consequences resulting from such use. The data should permit the official regulatory agencies a quick overview of the driver behavior and adherence to work time guidelines, safety regulations, and what is called in some jurisdictions "social regulations". This information should be available to the agencies during their examinations, which are generally conducted as random samplings or spot checks.
This type of information has in the past been gathered with so-called disk graphs (sometimes called tachograph charts or record charts) in the form of polar-coordinate hard copy disks which utilize the angular displacement as time. An analog radial displacement is indicative of such data as speed, distance, fuel consumption, engine rotation rates, etc. Such disk graphs have dispensed with the troublesome keeping of driving logs, and allow consistent recording of data such as speed, distance, fuel consumption, engine rotation rates, work-time data, driving time, ready periods, and rest times. These are accomplished on a real time or clock time basis in analog form. Such disk graphs or diaphragm disks are, per se, documents with high density information which is easy to handle, easily capable of being filed, and visually readable at all times. They are capable of mechanical evaluation, although at considerable cost. Such data carriers or data copies in the form of disk graphs are also distinguished by the fact that all driving data of a transportation commission, a shift, or a work day, can be overseen at a glance. Furthermore, in identifying each data carrier with a person or driver, the disk graphs are adapted in a particular manner to the requirements of the practice of motor vehicle transportation with respect to changes of driver in vehicle.
The weaknesses of systems using diaphragm disk or disk graph data carriers reside chiefly in the recordings themselves. The weaknesses are revealed during random spot checks of such data as rest periods to be observed, when one wishes to gather numerical information from the drive data recording in analog form on the disk graphs. These analog numbers are reliable to some extent. Any resulting errors can be prevented only with a substantial expenditure of time and evaluation experience. However, the reconstruction of the speed history of a vehicle before an accident situation is practically impossible. This is because the usual disk speed of one revolution per twenty-four hours, furnishes a relatively low resolution of the speed recordings, and requires considerable evaluation experience, and costly measuring instruments.
This compromise of fixing the recording time horizon, i.e. the overall recording time of a disk graph, at twenty-four hours is understandable for practical reasons. However, many jurisdictions have a legal requirement that the disks of the two preceding days must be available for inspection by the driving personnel, must be taken into account as a further disadvantage.
Moreover, acquiring drive data from a disk graph, fails to correspond to modern ideas concerning the handling of hard copy data. Thus, it is also understandable from this viewpoint, if the drivers have little affection for the tachograph in general. Aside from the fact that the driver must enter his personal data, and possibly other data, by hand before mounting the disk graph onto the tachograph, the tachograph must be opened, the disk graph must be threaded into the centering and carrying spindle, and the cover of the tachograph must be closed again. This assumes that the tachograph is equipped with a disk graph fastening arrangement which becomes effective automatically when the cover is closed. Otherwise, the fastening operation must be performed manually. If the vehicle's driver has a co-driver or "partner", as required depending upon regulations based on the tonnage or the distance to be driven, the insertion of the two required disk graphs becomes a relatively arduous and expensive procedure. It is a rather troublesome duty carried out in the morning in the cold, and usually poorly lighted driver cab. In addition, some care is required for handling of diagram disks because they must accommodate very fine speed recording traces, and are therefore equipped with a special recording layer which has the disadvantage of being sensitive to scratches and pressure.